Method for constructing an interaction circuit for a microwave tube

ABSTRACT

A method for constructing an interaction circuit for a microwave tube is disclosed. In the method, a metallic block has an elongated open-sided channel formed therein. The channel is transversely slotted with an array of slots. An array of apertured conductive plates are inserted into the array of transverse slots and a conductive cover is brazed over the open side of the channel to define therein an interaction circuit for a microwave tube. The method may be employed for fabrication of a circuit for a multicavity klystron tube, a coupled cavity slow wave circuit, and for a meanderline slow wave circuit.

United States Patent 91 James 51 Jan. 23, 1973 METHOD FOR CONSTRUCTING AN INTERACTION CIRCUIT FOR A MICROWAVE TUBE [75] Inventor: Bertram G. James, Redwood City,

Calif.

3,330,986 7/1967 Sililia ..3,-5/3.5 X 3,353,057 11/1967 Kato et al.... ..".3l5/3.5

3,383,620 5/1968 Forester ..315/3.5 X 3,390,451 7/1968 Peloscheck ..29/603 3,400,386 9/1968 Sinnott ....29/603 X 7 Primary Examiner-Richard .1 l-lerbst Assistant Examiner-Robert W. Church Attorney-Stanley Z. Cole and Leon F. Herbert [57] ABSTRACT A method for constructing an interaction circuit for a microwave tube is disclosed. In the method, a metallic block has an elongated open-sided channel formed therein. The channel is transversely slotted with an array of slots. An array of apertured conductive plates are inserted into the array of transverse slots and a conductive cover is brazed over the open side of the channel to define therein an interaction circuit for a microwave tube. The method may be employed for fabrication of a circuit for a multicavity klystron tube, a coupled cavity slow wave circuit, and for a meanderline slow wave circuit.

6 Claims, 7 Drawing Figures PATENTED JAN 23 I973 3 71 l. 943

FIG.I FIG.7

8 i --H-H-H-H-H-H-H- BERTRAM arm? I sa I ATTORNEY METHOD FOR CONSTRUCTING AN INTERACTION CIRCUIT FOR A MICROWAVE TUBE DESCRIPTION OF THE PRIOR ART Heretofore, microwave slow wave circuits of the meanderline or coupled cavity type have been constructed by milling a plate from opposite sides to define half of a cavity on each opposite side of a common wall portion separating the milled portions in the plate. Each milled plate included a central beam passageway and at least one wave energy communication slot through the common wall between each half of the cavity. The milled plates were then assembled with the beam passageways in axial alignment and the assembly was brazed to define the slow wave circuit. This turns out to be a relatively complicated and expensive way to construct slow wave circuits at high frequencies, such as X band or above, and does not facilitate inspection of the circuit once the circuit has been brazed together.

In another prior art method for fabricating microwave slow wave circuits, a slow wave circuit is formed by stacking an array of milled plates with spacing rings between adjacent plates. The inside wall of the spacer ring defines the side wall of each of the coupled cavities and the plates on opposite sides of the spacer ring define the end walls of the cavities and each end wall includes a central beam aperture. A curved wave energy communication slot is provided in each end wall. The plates and rings are stacked together and brazed to form the composite coupled cavity circuit. Such a circuit and method of fabricating same is disclosed in U.S. Pat. No. 3,297,906 issued Jan. 10, 1967, and assigned to the same assignee as the present invention. This method of fabricating the circuit has the same problem as the aforementioned method inasmuch as once the circuit has been brazed it is difficult to inspect.

It is also known from the prior art that the successive cavities for a klystron interaction circuit are constructed from a block of copper wherein an array of cavities are milled into the block from one side with the spacing between the milled cavities forming the end walls of the cavities. Once the cavities have been milled from one side a cover plate is brazed over the open side of the structure. Such a tube body and method of fabricating same are disclosed and claimed in U.S. Pat. No. 2,915,670 issued Dec. 1, 1959 and assigned to the same assignee as the present invention.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved method for constructing an interaction circuit for a microwave tube.

One feature of the present invention is the provision, in a method for fabricating a microwave interaction circuit, of forming an elongated channel in a conductive block, slotting the walls of the channel with an array of transverse axially spaced slots, inserting an array of apertured axially spaced conductive members into the array of transverse slots, and affixing a conductive cover over the open side of the channel to define the microwave circuit within the block.

Another feature of the present invention is the same as the preceding feature wherein the array of transverse members are brazed into the array of transverse slots in a first brazing step, and wherein the cover is brazed over the open side of the channel in a second brazing step performed after the first brazing step, whereby the brazed interaction circuit, after the first brazing step and before the second brazing step, is open for inspection.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view ofa metallic block which will form the body of the microwave tube,

FIG. 2 is a perspective view of the structure of FIG. 1 depicting a channel milled or otherwise formed in the block of FIG. 1,

FIG. 3 is a top view of the structure of FIG. 2 depicting an array of transverse slots intersecting the wall of the channel of FIG. 2,

FIG. 4 is an exploded view of the slotted block of FIG. 3 depicting the step of inserting the apertured plates into the transverse slots,

FIG. 5 is a top view of the structure of FIG. 4,

FIG. 6 is a view of the structure of FIG. 5 taken along line 6-6 in the direction of the arrows and showing the addition of a cover plate to the structure of FIG. 5, and

FIG. 7 is an end view of a conductive block depicting the channel to be formed therein and the cover to be brazed over the open side of the channel.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a conductive metallic block I, as of copper, in which the microwave interaction circuit for the electron microwave tube is to be formed. In the first step of the method of the present invention, (see FIG. 2) an elongated channel 2 of generally rectangular transverse cross section is formed in the block 1, as by milling. In a typical example for an X band tube, the channel 2 has a depth of approximately 0.700 inch and a width of approximately 0.700 inch.

'In the second step of the method, (see FIG. 3) the block is provided with an array of transverse slots 3 intersecting with the walls of the channel 2. The slots 3, as shown in FIG. 3, pass through both the bottom and side walls of the channel 2. In a typical example, the slots have a width for an X band tube, of approximately 0.090 inch. The spacing between adjacent slots 3 determines the period of the microwave circuit and can be formed with extremely high precision.

In the next step of the method, as shown in FIG. 4, an array of apertured plates 4, as of copper, are inserted into the array of slots 3 to define the common walls between adjacent coupled cavities of the microwave circuit to be formed in the block 1. The plates 4 each include a centrally disposed aperture 5 for passage of the beam therethrough. Two conical drift tube members 6 are brazed to the plate on opposite sides thereof to form reentrant drift tube portions projecting into the coupled cavities defined between adjacent plates 4. In addition, each plate 4 includes an elongated wave energy inductive coupling slot 7. In a preferred embodiment, the coupling slots 7 are axially aligned and provide mutual inductive coupling between adjacent coupled cavities of the slow wave circuit. In a typical example, inductive coupling slots, at X band, have a height of 0.125 inch and a length of 0.600 inch and the beam coupling holes have a diameter of approximately 0.125 inch.

After the plates 4 have been inserted into the slots 3, a pair of aligning blocks are inserted into the channel 2 at opposite ends of the array and an aligning rod is passed axially through the beam apertures 5 to obtain proper axial alignment of the beam apertures. Once the plates 4 have been assembled and aligned in the slots 3 within the block 1, the block with the plates is brazed such that the plates 4 are brazed to the side walls of the slots in the block 1 to form an integral structure.

The brazed structure is open on the top side as shown in FIG. 5. In a typical example at X band, the period of the circuit between midplanes of adjacent end walls 4 is approximately 0.290 inch. After the first brazing step has been completed the circuit is inspected to see that all the joints have been properly brazed. A conductive cover plate 8, as of copper, as shown in FIG. 6, is placed over the open side of the channel and cold tests are made on the circuit with microwave energy to assure that it has the proper microwave characteristics such as bandwidth, etc. Once the microwave characteristics have been checked, the cover plate 8 is brazed, in a second brazing step, over the open side of the channel to complete fabrication of the microwave interaction circuit. The cover plate 8 is brazed to the adjacent side edges of the plates 4 and block 1.

Fabrication of the microwave interaction circuit according to the method as above described greatly facilitates construction of the circuit inasmuch as the transverse slots can be positioned with high accuracy and the plates 4 can be formed with high accuracy. Once the unit is assembled, except for the cover plate, the brazed circuit is open for inspection for detecting any flaws therein. After the cover is placed on the circuit, its microwave characteristic can be checked and if necessary the cover can be removed and alterations made. AFter the second brazing step, if it is found that the circuit is defective, the plate 8 can be sliced from the block 1 to open the circuit, the circuit can be modified and a new plate 8 brazed over the open side of the channel to complete the circuit.

Referring now to FIG. 7 there is shown an alternative embodiment of the present invention wherein the block 11 which is to have the channel formed therein is not of rectangular cross section but includes a longitudinal ridge 12 of generally rectangular cross section which is equivalent to the block 1 of FIG. 1. The cover plates which is eventually brazed over the open side of the channel 2 has a longitudinal channel 13 formed therein which is brazed to the top and sides of the ridge 12 for closing the circuit.

Since many changes could be made in the above construction and many apparently widely different cmbodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a method of constructing at least a portion of a vacuum enclosure of a linear electron beam microwave tube having a series of cavities provided with straight cross sectional sides wherein the cross section is taken perpendicular to the longitudinal axis of the tube, the steps of:

forming an elongated channel in a conductive block,

said channel extending along said axis of said tube and having straight cross sectional sides perpendicular to said axis;

forming a series of transverse axially-spaced pairs of slots in the opposite walls of said channel;

forming each of a plurality of conductive members with an aperture for providing communication for said electron beam therethrough;

inserting one of said members into each of said pairs of slots;

axially aligning said beam apertures;

brazing each of said members into sealed assembly with its respective pair of slots to form said series of said cavities in a first brazing step, each of said cavities having an open side, and

in a subsequent step, brazing a conductive cover over said cavities into sealed assembled relationship with said channel to form said series of cavities and said vacuum enclosure portion.

2. The method of claim I wherein each of said apertured members includes,

an elongated slot for providing wave energy communication therethrough at the operating frequency of the tube, and

including the step of axially aligning the wave energy communication slots in said array of members.

3. In a method of constructing at least a portion of a vacuum enclosure of a coupled cavity traveling wave tube having cavities provided with a selected cross section taken perpendicular to the longitudinal axis of the tube, wherein said cross section consists of straight sides, the steps of:

forming an elongated channel in a conductive block,

said channel extending along said axis of said tube and having said selected cross section;

forming a series of transverse axially spaced pairs of slots in the opposite walls of said channel; forming each of a plurality of conductive members with an electron beam aperture and an opening for providing wave energy communication therethrough at the operating frequency of the tube;

inserting one of said members into each of said pairs of slots;

axially aligning said beam apertures;

brazing each of said members into sealed assembly with its respective pair of slots to form a series of said cavities in a first brazing step, each of said cavities having an open side;

detachably mounting a conductive cover over the open side of said cavities;

testing the microwave characteristics of said cavities;

and

brazing said cover over said cavities into sealed assembled relationship with said channel to form said coupled cavities and said vacuum enclosure portion.

4. The method of claim I, which further includes the steps performed after the first brazing step and before the second brazing step of:

detachably mounting a conductive cover over the open side of said cavities, and

testing the microwave characteristics of said cavities.

5. The method of claim 3, in which said selected cross section is square. 5

6. The method of claim 3 in which said selected cross section is rectangular. 

1. In a method of constructing at least a portion of a vacuum enclosure of a linear electron beam microwave tube having a series of cavities provided with straight cross sectional sides wherein the cross section is taken perpendicular to the longitudinal axis of the tube, the steps of: forming an elongated channel in a conductive block, said channel extending along said axis of said tube and having straight cross sectional sides perpendicular to said axis; forming a series of transverse axially-spaced pairs of slots in the opposite walls of said channel; forming each of a plurality of conductive members with an aperture for providing communication for said electron beam therethrough; inserting one of said members into each of said pairs of slots; axially aligning said beam apertures; braziNg each of said members into sealed assembly with its respective pair of slots to form said series of said cavities in a first brazing step, each of said cavities having an open side; and in a subsequent step, brazing a conductive cover over said cavities into sealed assembled relationship with said channel to form said series of cavities and said vacuum enclosure portion.
 2. The method of claim 1 wherein each of said apertured members includes, an elongated slot for providing wave energy communication therethrough at the operating frequency of the tube, and including the step of axially aligning the wave energy communication slots in said array of members.
 3. In a method of constructing at least a portion of a vacuum enclosure of a coupled cavity traveling wave tube having cavities provided with a selected cross section taken perpendicular to the longitudinal axis of the tube, wherein said cross section consists of straight sides, the steps of: forming an elongated channel in a conductive block, said channel extending along said axis of said tube and having said selected cross section; forming a series of transverse axially spaced pairs of slots in the opposite walls of said channel; forming each of a plurality of conductive members with an electron beam aperture and an opening for providing wave energy communication therethrough at the operating frequency of the tube; inserting one of said members into each of said pairs of slots; axially aligning said beam apertures; brazing each of said members into sealed assembly with its respective pair of slots to form a series of said cavities in a first brazing step, each of said cavities having an open side; detachably mounting a conductive cover over the open side of said cavities; testing the microwave characteristics of said cavities; and brazing said cover over said cavities into sealed assembled relationship with said channel to form said coupled cavities and said vacuum enclosure portion.
 4. The method of claim 1, which further includes the steps performed after the first brazing step and before the second brazing step of: detachably mounting a conductive cover over the open side of said cavities, and testing the microwave characteristics of said cavities.
 5. The method of claim 3, in which said selected cross section is square.
 6. The method of claim 3 in which said selected cross section is rectangular. 